Structure of metal container having trunk pipe and branch pipe, and manufacturing method and apparatus therefor

ABSTRACT

A welded metal container for a sheath 1 or 1A of gas insulated switch gear comprises a trunk pipe 2, 21 and a branch pipes 3, 31, 32 welded to the trunk pipe 2,21 by arc welding A or laser beam welding LB and flanges welded to the each end portion of the trunk pipe 2, 21 and branch pipes 3, 31, 32 by the laser beam welding. After the arc welding A, the ends of trunk pipe 1, 21 and branch pipes 3, 31, 32 are machined precisely and flanges 4a, 4b, 4c, 4d, 4f and 4g are welded to the end portions of the trunk pipe 2, 21 and branch pipes 3, 31, 32.

This application is a division of application Ser. No. 07/760,890, filedSep. 17, 1991, now U.S. Pat. No. 5,444,206 issued Aug. 22, 1995.

BACKGROUND OF THE INVENTION

The present invention relates to a metal container having a trunk pipeand branch pipe, such as a sheath of gas insulated switch gear, and moreparticularly, to a structure of welded metal container having a trunkpipe and branch pipe welded thereto and flanges welded to the each endportion of the trunk pipe and branch pipe, and manufacturing method andapparatus therefor.

During manufacturing, a metal container having a trunk pipe and branchpipe, for example, a sheath of gas insulated switch gear which has aplurality of pipes welded to the trunk pipe, it is necessary toaccommodate weld flanges to end portions of the branch pipe and trunkpipe. However arc welding is used for the above purpose. In the welding,however, this arc welding requires a complete penetration welding so asto ensure the gas-tightness. The flange faces have to be machined afterwelding when an accuracy is required. Laser welding is used for joiningpipe and flanges, as disclosed in Japanese laid-open patent publicationNo. 59-189092/1984, Processing of LAMP '87, Osaka, May, 1987, pages157-162, "Deep Penetration Welding with High Power Co Laser", HIRAMOTOet al, and Mitsubishi Denki Giho, No. 10, 1989, page 37-40.

The aforementioned prior art pays no attention to the working method, inwhich the joint between the flanges and trunk pipe is merely changedfrom the arc welding to the laser welding. No consideration is takeninto the structure and manufacture of the actual metallic containers,namely the widely used metal container having a branch pipe such as thegas insulated switch gear sheath having branch pipes. Therefore, arcwelding is still used for manufacturing the metallic container having aplurality of branch pipes.

When the trunk pipe and the flange are bonded by arc welding, the flangemay fall down due to the welding heat and a restraint or support must beprovided.

For example, with the following welding conditions:

diameter of the trunk pipe: 600 mm,

length of the trunk pipe: 2,000 mm,

thickness of the trunk pipe: 6 mm-12 mm,

weld width (bead width): 6 mm-8 mm,

the welded flange is inclined or drops by about 2 mm. Therefore,inaccurateness in the degree of parallelization and perpendicularityoccurs. In order to enhance the accuracy of the container, the flangehave to be machined after welded, and the machining results createsproblems.

Unless the ends of the branch pipe and the trunk pipe are preciselymachined after welding, it is difficult to weld the trunk pipe to theflanges. This makes it necessary to machine the ends, but the flangesare inevitably deformed when welded. Therefore, it is necessary tomaintain the accuracy of the flange by machining the same so as to setthe flatness of the flange surface and distance between flanges tosuitable levels and to eliminate the inclination of the flange surfaceafter welding operation. This raises a serious problem duringproduction.

The prior art requires a large-sized machine for machining the flangesfor a large container. This necessity dilutes the effects ofaccomplishing the machine before the welding. However, this dilution isnot taken into consideration to raise another serious problem in case ofthe large sized container.

In addition, in conventional techniques, a recess of 0.2-3 mm in depthis provided in the flange, and an end portion of the pipe is inserted inthis recess. A laser beam is applied to the portion to be welded, in thedirection to carry out the laser welding of the workpieces whilerotating the same.

The angle at which the laser beam is applied to the surfaces to bewelded is about 3°-20°. That is, a laser beam is applied diagonally tothe surfaces to be welded. Therefore, the depth of penetration of theflange and pipe is uneven, and perfect penetration bead weld cannot beobtained in some cases in one pass.

In general, the outer diameter of a pipe has tolerance of ±1% accordingto the Japanese Industrial Standards. Therefore, even when a recess of anominal pipe diameter is cut in one surface of a flange, it becomesdifficult to insert a pipe, the outer diameter of which has certaintolerance, in the recess in the flange or a clearance between the pipeand recess becomes large even if the pipe fits in the recess, so thatsuch flange and pipe become in some cases unsuitable for welding.

Accordingly, if a pipe of about 50 mm (about 2 inches) in diameter iswelded to a flange by using the above-described conventional weldingtechniques, the pipe can be inserted in the recess in the flange due tothe small tolerance of this diameter and the welding can be carried out.However, when a large-sized pipe having a diameter of, for example,around 744 mm is used, the welding thereof to a flange cannot be donesuitably in many cases since this pipe has tolerance of as large as ±7.4mm.

A laser machining apparatus for cutting or welding a workpiece by makinguse of a laser beam from a laser oscillator is disclosed in, forexample, Japanese Laid-Open Patent Publication No. 60-227987/1985.

A machining table is sequentially arranged thereon with a welding head,a cutting head and a heat treatment head and is underlaid by a laseroscillator so that the workpiece can be moved in the same direction as alaser beam outputted from the laser oscillator. Moreover, the weldinghead and the cutting head on the machining table can be moved at a rightangle with respect to the output direction of the laser beam.

In machining application of the workpiece, either the welding head orthe welding head and the cutting head are moved at a right angle withrespect to the output direction of the laser beam so that the laser beammay not be obstructed but can enter the machining head. The workpiece isso moved that the workpiece may be positioned just below the machininghead in operation.

Since the individual machining heads are independently fixed on themachining table in accordance with the prior art, the machining headshave to be moved each time according to the machining application of theworkpiece, and the workpiece must be positioned just below the machininghead in accordance with the machining application, thus raising aproblem in the machinability. Moreover, the individual machining headsmay be spaced at distances for accommodating small or large workpieces.As a result, a problem arises in that the system is of a large size.When the machining head once moved is returned to its initial positionbefore a predetermined machining, it is necessary to align the opticalaxis of the laser beam coming from the laser oscillator and the centerof a bend mirror which is disposed in the machining head to change thepath of the aforementioned laser beam. This alignment is difficult, andit is seriously troublesome to position the moved machining head foreach machining. Moreover, the aforementioned prior art does not takeinto consideration the cutting of the end face of the tubular containersuch as the bus of the gas insulation control apparatus nor into thecorrection of that gap between the pipe end and the flange groove, whichnever fails to occur in the actual welding, and the correction of thedislocation.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a welded metalcontainer, such as a sheath of an insulated switch gear, in whichflanges are highly accurately joined, with a reduced number of steps tothe individual ends of the trunk pipe and the branch pipe bonded to thetrunk pipe by the welding operation.

To accomplish the object of the present invention, there is provided awelded metal container in which a metallic trunk pipe, and a branch pipebranched axially from the trunk pipe, are welded by arc welding or laserbeam welding and in which flanges to be joined to the individual ends ofthe branch pipe and the trunk pipe are welded by a laser beam.

Another feature of the present invention resides in providing a methodof producing tubular containers, capable of minimizing the weldingdeformation of even a branch pipe-carrying container in which flangesare joined to the end portions of a trunk pipe and branch pipes,reducing the time required for with a machining operation, which iscarried out after the welding of flanges to pipes in a conventionalmethod of this kind, omitted, and thereby obtaining a highly accuratewelded tubular container.

The object of the present invention is achieved by joining a trunk pipeand a branch pipe to each other by arc welding, mechanically cutting orlaser cutting the end surfaces to which flanges are to be joined of thetrunk and branch pipes, and joining by laser welding alreadymechanically processed flanges to the end surfaces of the processedtrunk and branch pipes.

According to the present invention, a trunk pipe and a branch pipe arethermally deformed when they are joined together by arc welding.However, after the deformed portions are mechanically processed toincrease the accuracy of the pipes to a proper level, flanges can bejoined to the end portions of the same pipes by laser beam welding whichcauses minimum thermal deformation. Therefore, it is unnecessary tocarry out a machining process after the pipes and flanges are finallywelded, and a highly accurate tubular container can be obtained in lesstime. Especially, in the case of production of a sheath for a deviceformed by combining a plurality of machines, such as a gas insulatingswitch device, these advantages are more markedly displayed.

A further object of the present invention is to provide the techniquesfor butt-welding two members, capable of obtaining a perfect penetrationbead in one pass.

The object of the present invention can be achieved by a welding method,wherein two parallel surfaces of two members are brought into abutmentand welded to each other, wherein a surface to be welded, which projectsrelatively from a surrounding surface, of one member and a surface to bewelded of another member are abutted on each other, with heat being thenapplied from a position on a plane including the surfaces to be weldedto the same surfaces in the direction substantially parallel to thesurfaces to be welded, whereby the surfaces are welded to each other.

Other object of the present invention can be achieved by a pipe weldingapparatus comprising a fixed base, a rotating means provided on thefixed base, a rotary body adapted to be rotated by the rotating means,and a driving means provided on the rotary body and adapted to support atubular material to be welded at its both end opened portions and drivethe material, the axis of rotation of the rotary body and that of thetubular material driven by the driving means crossing each otherperpendicularly, the axis of rotation of the rotary body and that of thetubular material being aligned with each other when the rotary body isrotated.

When two members are brought into abutment and welded to each other, theportion of one member which is adjacent to the surface thereof to bewelded is tapered in advance.

Due to this tapered part, the welding heat can be applied from aposition on a plane including the surfaces to be welded to thesesurfaces in the direction parallel to the same surfaces.

The surfaces to be welded are disposed on one plane, and do not on notless than two planes.

Therefore, the depth of penetration becomes uniform in the portions oftwo members which are in the vicinity of the surfaces to be welded.

When the members to be welded have not less than two surfaces to bewelded the perpendiculars of which cross each on the at right angles asin a case where flanges are welded to each of two perpendicularlycrossing unitarily combined pipes, one surface to be welded is weldedfirst as the relative member is rotated around a line perpendicular tothe same surface, i.e. the axis thereof. Another surface to be welded isthen welded as the relative member is rotated around a lineperpendicular to the same surface, i.e. the axis thereof.

If the welding is thus carried out in order, members having not lessthan two surfaces to be welded which have a predetermined angletherebetween can be welded with a high efficiency.

A further object of the present invention is to provide a lasermachining system which is suited especially for cutting the end of atubular container and for welding the tubular container and a flange notby moving the workpiece in accordance with the machining application butby using a laser beam for a series of continuous machining operations bydevising the machining heads.

Yet anther object of the present invention is to provide a lasermachining system for achieving the above-specified object by correctingthe gap between the pipe end and the flange groove and the dislocationand a machining apparatus for performing the cutting and weldingoperations easily in accordance with the machining application of theworkpiece and a positioning device capable of correcting either the gapbetween the pipe end and the flange groove or the dislocation easilyeven when the flange is to be welded to the end of a tubular container.

According to the present invention, a laser machining system comprisesconveyor means for conveying a workpiece to be machined, a laseroscillator for oscillating a laser beam for machining said workpiece onthe conveyor means, a beam guide for guiding the laser beam emitted fromthe laser oscillator and including a bend mirror for changing the pathof the laser beam, and a plurality of machining heads adapted to beinterchanged in accordance with the machining application of theworkpiece for irradiating an identical position on the woekpiece withthe laser beam which has its path changed in an identical position andis guided by said beam guide.

A laser machining system of the present invention arranges the pluralityof machining heads concentrically with respect to a pivot axis of adisc, with the plurality of machining heads being disposed about thecircumference of the disc and being selectable in accordance with themachining application of the workpiece by turning said disc.

A laser machining system of the present invention may comprise conveyormeans for conveying a tubular container having its end portion assembledwith a flange, a laser oscillator for oscillating a laser beam to cutsaid tubular container on said conveyor means or weld the same to saidflange, and a beam guide for guiding the laser beam outputted from saidlaser oscillator. The cutting and welding heads may be adapted to bemoved in accordance with the cutting operation of the tubular containeror the welding operation to said flange for irradiating the laser beam,which is guided by said beam guide, to execute the cutting operation ofthe tubular container or the welding operation to the flange.

According to the present invention, a machining apparatus is providedwhich includes a rotary disc, a plurality of machining heads arrangedconcentrically at a predetermined spacing on a circumference of a rotarydisc for irradiating a workpiece to be machined with a laser beam comingfrom a laser oscillator through an optical system to machine theworkpiece, with drive means rotatably driving the rotary disc with saidmachining heads, wherein the optical axis of the laser beam coming fromthe laser oscillator and the optical axis of the optical system of themachining heads on the rotary disc are aligned with each other.

According to the present invention, a positioning device comprises awidth adjusting mechanism for correcting the axial gap of the abuttingportions of tubular members to be welded, with a pipe expandingmechanism being provided for correcting the radial dislocation of theabutting portions of the tubular members, and with a turn mechanism forturning the tubular members while being expanded by the pipe expandingmechanism.

A machining head x according to the present invention, may comprise agenerally cylindrical nozzle for guiding a laser beam from a laseroscillator in the vicinity of a workpiece to be machined; a condensinglens disposed midway in the nozzle for condensing the laser beam toirradiate the workpiece with the condensed laser beam; and shield gasintroducing means for introducing a shield gas which is used to shieldthe laser beam in the nozzle against a wall surface and which is to besprayed toward the workpiece while guiding the laser beam, wherein thenozzle has a variable aperture at tip thereof and

The laser machining system of the present invention may also comprisefirst conveyor means for conveying a trunk pipe having a branch pipefixed in advance to its predetermined portion; a cutting station forcutting the branched trunk pipe conveyed by the conveyor means; a flangeassembling station for assembling each of those ends of the branchedtrunk pipe conveyed by said first conveyor means, which were cut at thecutting station, with the flange which is conveyed by the secondconveyor means being arranged generally at a right angle with respect tosaid first conveyor means; and a welding station for welding each ofthose ends of the branched trunk pipe conveyed by the first conveyormeans, which were assembled with a flange at the flange assemblingstation, and the flange-assembled portion of the same with a laser beam.

In the laser machining system of the present invention, when theworkpiece being conveyed on the conveyor means comes to a predeterminedposition, it is irradiated with the laser beam so that it may besubjected to a predetermining machining such as the welding or cutting.Then, the workpiece can be continuously welded or cut in an identicalposition merely by interchanging, selecting or rotationally moving theplural machining heads in accordance with the machining application ofthe workpiece itself. Moreover, the branched trunk pipe is cut at itsend by means of the laser beam, before the flange is attached thereto,and its portion to be assembled with the flange is welded by the laserbeam. As a result, no machining is required after the welding operationso that the machining operations can be continuously accomplished.

In the machining apparatus of the present invention, the pluralmachining heads are arranged along the circumference of a rotary disc,with the machining heads being concentric to the pivot of the rotarydisc, with a fixed rotational drive system. As a result, the opticalaxis of the laser beam and the optical axis of the optical system of themachining head can be aligned to prevent the laser beam from coming outof focus.

In the positioning device of the present invention, furthermore, theaxial gap of the abutting portions of the tubular members to be weldedis corrected by the width adjusting mechanism, and the radialdislocation of the abutting portions of the tubular members is correctedby the pipe expanding means. At the same time, the tubular membersexpanded by the aforementioned pipe expanding means can be rotated bythe rotating mechanism. As a result, the axial gap and the dislocationof the abutting portions can be reliably corrected to ensure the laserbeam welding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a welded metalcontainer constructed in accordance with the present invention;

FIG. 2 is a perspective view of another embodiment of a welded metalcontainer constructed in accordance with the present invention;

FIG. 3 is a longitudinal sectional view of the welded metal container ofFIG. 2;

FIG. 4 is a sectional view of a joined portion of the trunk pipe end andthe flange;

FIG. 5 is a sectional view of a joined portion of the branch pipe endand the flange;

FIG. 6 is a schematic top plan view of a gas insulated switch gearaccording to the present invention;

FIG. 7 is a front elevational view taken along the line VII--VII in FIG.6;

FIG. 8 is a flow chart showing the production of the pressure containerfor a gas insulated switch gear, which constitutes an embodiment of themethod of producing a tubular container according to the presentinvention;

FIGS. 9a-9c are sectional views of various shapes of welded joints usedfor a tubular container constructed in accordance with the presentinvention;

FIGS. 10 and 11 are schematic views of methods of cutting a pipe andsurface in a tubular form in accordance with the present invention;

FIGS. 12a-12c are sectional views illustrating the steps of welding thepipe and a flange to each other by a welding method of the presentinvention;

FIG. 13 is a partial sectional view illustrating an applied example of awelding method of the present invention;

FIGS. 14 and 15 are schematic views of a welding apparatus of otherembodiments of the present invention;

FIG. 16 is a perspective view showing one embodiment of a lasermachining system constructed in accordance with the present invention;

FIG. 17 is a front elevational schematic view of a machining apparatusused in the laser machining system of the present invention;

FIG. 18 is a top plan view of FIG. 17;

FIG. 19 is a sectional view of a positioning device used with the systemof the present invention;

FIG. 20 is a side elevational view taken in a direction of the arrow Tin FIG. 19;

FIG. 21 is a detailed sectional view of a portion of the abuttingportions of the trunk pipe and a flange;

FIG. 22 illustrates a dislocation measuring method of an edge aligningmechanism according to the present invention;

FIGS. 23a-23c are schematic views of the steps of attaching the trunkpipe and the flanges;

FIG. 24 is a view taken along the line XXIV--XXIV in FIG. 17;

FIG. 25 is a schematic view of the machining system of the presentinvention with a small aperture;

FIG. 26 is a view taken in the direction of the line XXVI--XXVI in FIG.25;

FIGS. 27a-27d are perspective views of the machining steps when theflanges are to be attached to the branch trunk pipe; and

FIG. 28 is a perspective view of another embodiment of a laser machiningsystem constructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1 sheath 1 used for a gas insulated switch gear iscomposed of a trunk or main pipe 2, branch pipes 3 and 31 joinedgenerally at a right angle with respect to the axial direction of thetrunk pipe 2, by an arc welding A, flanges 4a and 4b joined to the twoends of the trunk pipe 2, flanges 4c and 4d joined to the ends of thebranch pipes 3 and 31. The sheath 1 is constructed by bonding the trunkpipe 2 to the flanges 4a and 4b and bonding the branch pipes 3 and 31 tothe flanges 4c and 4d by the laser beam welding LB.

In the embodiment of FIG. 1, the thermal deformations by the arc weldingA are solved by carrying out the laser beam welding after the arcwelding A. After the arc welding A, end portions of the trunk pipe 2 andbranch pipes 3 and 31 are machined presicely and flanges 4a, 4b, 4c and4d are welded to the end portions of the trunk pipe 2 and branch pipes 3and 31 by the laser beam welding LB. As a result, the sheath 1 obtainedcan be highly accurate and the workability and the assembly accuracy canbe improved in assembling the sheath 1.

For example, when the following conditions of the welding,

diameter of the trunk pipe: 600 mm,

length of the trunk pipe: 2,000 mm,

thickness of the trunk pipe: 4.5 mm-12 mm,

weld width (bead width): 2 mm-3 mm,

Laser output: 5 Kw-10 Kw

the flange welded by the laser beam is inclined or falls down by around0.3 mm. Therefore, accurateness in the degree of parallelization andperpendicularity is sustained.

In FIGS. 2 and 3 showing a second embodiment, a sheath 1A comprises atrunk pipe or trunk pipe 21, a branch pipe 32 joined to the trunk pipe21, the flanges 4e, 4f and 4g joined individually to the two ends of thetrunk pipe and the end of the branch pipe 3 and or supports 5 and 51.

In the embodiment of FIGS. 2 and 3, the laser beam welding LB is appliedto the joints between the trunk pipe 21 and the flanges 4e and 4f,between the branch pipe 32 and flange 4g, between trunk pipe 21 and thestays 5 and 51, and between the trunk pipe 21 and the branch pipe 32.Particularly, in the embodiment of FIGS. 2 and 3 the arc welding A iscarried out in advance, and thereafter a highly accurate welding isperformed by the laser beam welding. Therefore, a highly accuratetubular container can be easily provided.

The laser beam welding is not suitable in applying to an corner portion.In the embodiment of FIGS. 2 and 3, the end portion of the branch pipe32 is flared in advance, and the branch pipe 32 is bonded to the trunkpipe 21 by the laser beam welding LB. As a result, it is easy to applyan automatic welding system with a low strain and to produce a highaccurate sheath.

Incidentally, the sections of the joints between the flange 4e and thetrunk pipe 21 and between the flange 4g and the branch pipe 32 are shownin detail in FIGS. 4 and 5, respectively. As shown, not only the end ofthe trunk pipe and the flanges 4e, and the end of the branch pipe 32 andthe flanges 4g are welded by the laser beam, but also the corners arefillet-welded from the inside and outside by the laser beam welding LB.Thus, the misalignment of the flanges 4e and 4g is reduced in comparisonwith those of the arc welding and the cost required in pre-straining,shaping, and machining works after the welding operations is reduced.

FIG. 6 and 7 show an example, in which the present invention is appliedto a gas insulated switch gear (GIS). The GIS is constructed of abreaker 11, a disconnector 13, an arrester 14 and a single phase bus 15.In these units, a trunk circuit conductor 17 of three phase bus 16 issupported by an insulator in the sheath 1 having the welded structureshown in FIG. 1 and has a structure in which a space is sealed withhighly insulating SF gases. The individual units are connected throughthe flange 4a to 4g of the individual sheath 1 by bolts. Usually, thecontainers are sealed with the SF gases under 4 to 5 atms. Thisconfinement may be performed at the time of installation. The flanges 4ato 4g of the sheath 1 are required to have both a flatness for ensuringthe contactness thereof and effecting the sealing properties of anO-ring and the rectangularities with respect to the flanges 4c, 4d and4g of the branch pipes 3, 31 and 32 which extend at a right angle fromthe other sheath 1 positioned below the trunk pipe 2 and 21 on the axisof the breaker 11 and covering the conductor 17 of the trunk bus andwith respect to the flange 4a, 4b, 4e and 4f of the last-mentioned trunkpipe 2 and 21 of the other sheath 1.

In the present embodiment, the sheath for accommodating each deviceadopts the structure, in which the trunk pipe and the flanges, and thebranch pipe and the flanges are welded by the laser beam welding. As aresult, the aforementioned accuracy can be easily achieved to improvethe efficiency of the assembly.

FIG. 8 shows a flow chart of the production process of the sheath 1 and1A (container) for a GIS as shown in FIGS. 1 and 2. A sheath for a GISis divided into four members, i.e. a trunk pipe 121, a branch pipe 122,trunk pipe flanges 109 and a branch pipe flange 110. Each member isprepared independently, and a bore for connecting the branch pipe 122 ismade in the trunk pipe 121 in a subsequent step. The branch pipe is cutso that the shape of a joint end portion thereof corresponds to that ofthe bore made in the trunk pipe 121. Connecting bores are made in trunkpipe flanges 109 and a branch pipe flange 110, these flanges being thensubjected to surface finishing and a process corresponding to the use ofthe sheath. The trunk pipe 121 and branch pipe 122 are then joinedtogether by arc welding, and the end portion of the arc welded trunkpipe 121 and the branch pipe 122 are cut by the laser beam or machinedin a subsequent step as shown in FIG. 8. The bored and surface finishedtrunk pipe flanges 109 and the branch pipe flange 110 are then joined bylaser welding to the laser cut or machined end portions of the trunkpipe 121 and branch pipe 122 to produce a tubular sheath.

As welded structural members, as shown in FIG. 9a, 9b and 9c, a T-shapejoint in which a pipe end is welded to an end surface of a flange, and abutt joint in which pipe ends are abutted on and welded to each other.Since the bevel portions of these joints are mechanically processed asshown in the drawings, the accuracy of the joints is improved, and thelaser welding can be applied. This can prevent the welding deformationof the joints. Accordingly, even when a flange including a surfacethereof to be sealed is mechanically processed in advance, and thenwelded by laser beam, the function of a sealed sheath can be sustained.

When the direction and size of the flange surface do not require a highaccuracy with respect to a trunk pipe 101, as in a branch pipe forconstituting a manhole, the branch pipe 12 and flange member 13 forforming the manhole are joined together in advance by arc welding, andthe manhole-forming flange 113 is then mechanically processed. Theresultant flange 113 is arc welded to the trunk pipe 1, and a productthus obtained is then subjected to the same steps as shown in FIG. 8.

FIG. 10 shows an example of a means for cutting an end surface of thepipe shown in FIG. 8, in which the end portion of a branch pipe-carryingtrunk pipe 221 is cut by applying the laser beam from a laser oscillator214 to the end surface via a processing head 215 while tuning the branchpipe-carrying trunk pipe 230. The workpiece is positioned by apositioner 240.

FIG. 11 shows an example of a means for cutting an end surface of thepipe shown in FIG. 8, in which the end portion of a branch pipe-carryingtrunk pipe 230 is cut by applying the laser beam to the end surfacewhile turning a laser processing head 152. The advantage of the lasercutting resides in that a highly accurate cut surface can be obtained bymaking a full turn of an object pipe or processing head irrespective ofthe cutting length of a pipe end surface.

According to this embodiment described above, a flange can bemechanically processed in the form of a single part. Therefore, a flangecan be processed singularly in an intensive manner, and a comparativelysmall-sized processing machine can be used. This enables the set up timewhich is not included in the cutting time to be saved.

Since the pipe member plate working and welding step and flangemachining step can be carried out simultaneously, the sheath producingperiod can be reduced by about 40%. In addition, the time required for apipe shaping operation carried out after a branch pipe is welded to atrunk pipe can also be reduced by about 50-70% since the bending of thetrunk pipe and the inclination of the branch pipe can be eliminated bythe mechanical processing or laser cutting of the pipe end surface.

FIGS. 12a, 12b, and 12c are sectional views showing the steps of weldinga pipe 301 and a flange 302 to each other by a welding method. FIG. 13is a sectional view illustrating an example to which the welding methodof this embodiment is applied.

FIG. 12a shows the condition of the pipe 301 and flange 302 not yetsubjected to a welding process. The two surfaces 302a and 302b of theflange are parallel as shown in the drawing.

FIG. 12b shows the flange 302 tapered by cutting off the portion thereofshown by broken lines 303. If the flange 302 is processed in thismanner, the surface thereof, opposed to a surface 306b of the pipe 301to be, becomes parallel at a portion 306a to be welded thereof to thesurface 306b. The angle of inclination of this tapering surface is about9°.

FIG. 12C shows the tapered flange 302 and pipe 301 abutted on and laserwelded to each other. Since the flange 302 is tapered, a laser beam canbe applied in the direction of an arrow 304 to the surfaces 306a and306b to be welded. As a result, the depth of penetration 305 shown by abroken line of the welded surfaces 306a and 306b become substantiallyuniform. If the flange and pipe are machined at their surfaces to bewelded to a predetermined surface accuracy and then subjected towelding, there can be complete penetration with one pass.

Even when the outer diameter of the pipe has tolerance, the surfaces306a, 306b to be welded of the flange 302 and pipe 301 have no clearancetherebetween. Therefore, a stable laser welding operation can be carriedout.

FIG. 13 is a sectional view of a principal portion of a branchpipe-carrying pressure container 330, an example to which the aboveembodiment is applied.

This pressure container 330 is a pressure container for a GIS used for agas insulating transformation machine which is used with an insulatinggas, such as SF gas sealed therein.

The pressure container 330 includes two perpendicularly crossing pipes331, 333, and flanges 332a, 332b, 333a welded to the end surfaces ofthese pipes 331, 333.

If the welding method of the embodiment described in FIGS. 12a to 12c isused for welding the flanges 332a, 332b and 333a to the pipes, they canbe laser welded reliably and the leakage of the insulating gas can beprevented.

The welding apparatus 340 of FIG. 14 is provided with a fixed base 341,a rotary unit 342 and 342' set on the fixed base 341, a rotary disc 343adapted to be rotated by the rotary unit 342, and two opposed rotaryunits 344, 345 set on the rotary disc 343, and the axis of rotation ofthe rotary disc and that of rotation of a member rotated by the tworotary units 344, 345 cross each other perpendicularly.

A material to be welded is set as a member rotated by the two rotaryunits 344, 345, and three flanges 348, 349, 350 are laser welded to theend surfaces of two perpendicularly crossing pipes 346, 347 as shown inthe drawing.

The apparatus for laser welding these parts includes a laser oscillator351, a bending mirror 354 adapted to change the path of a laser beam 352emitted from the laser oscillator 351, and a processing head 353 adaptedto apply a laser beam 355, the path of which has been changed, to thesurfaces to be welded.

An operation of welding the pipes 346, 347 and flanges 348, 349, 350 toeach other by using this apparatus will now be described.

The path of the laser beam 352 outputted from the laser oscillator 351is changed by the bending mirror 354, and the resultant laser beam isintroduced into the pivotable processing head 353. A condensed laserbeam 356 is applied in the perpendicularly downward direction to agroove between the tapering flange 350 and pipe 347 to weld the same.

In this case, the pipe 347 is rotated in the direction a by therotational movements of the rotary units 344, 345, whereby thefull-circled welding of the flange 350 and pipe 347 can be carried out.

The welding of the flange 343 and pipe 347 is carried out by turning therotary disc 348 in a 180-degree arc, and then applying a laser beam 356to the flange 348 and pipe 347.

If one more laser oscillator is provided, the flange 348, 350 can bewelded at once to the pipe 347.

In order to weld the flange 349 to the pipe 346, the processing head 353is turned up in a 90-degree arc to be set in a horizontal position shownby a two-dot chain line, and a laser beam is then applied to thesurfaces to be welded.

When the rotary disc 343 is rotated by using the rotary unit 342, 342'in this case, the pipe 346 is rotated in the direction β to enable thefull-circled welding of the pipe 346 and flange 349 to be carried out.

When the welding apparatus 340 of the second embodiment is used, thelaser welding of a flange and a pipe of a branch pipe-carrying tubularpressure container can be easily carried out.

FIG. 15 illustrates other welding method which is used to laser weld aflange and a pipe of a branch pipe-carrying tubular pressure container.

The shape of this branch pipe-carrying tubular pressure container 471 issubstantially identical with that of the branch pipe-carrying tubularpressure container shown in FIG. 13, and the container 471 has twopipes, i.e. a pipe 465, and a pipe (extending at right angles to thesurface of FIG. 15) crossing the pipe 465 perpendicularly, therespective end portions of these pipes being adapted to be subjected tolaser welding for joining flanges 462, 463, 464 thereto.

An apparatus for laser welding these flanges to the pipes is providedwith an oscillator 467, and a rotary processing head 66 adapted to applya laser beam emitted from the the oscillator 467 to the surfaces to bewelded, and this rotary processing head is adapted to be rotated in thedirection of an arrow 469.

A rotary unit 461 is adapted to rotate the branch pipe-carrying tubularcontainer 471 freely and substantially horizontally.

The operation of each apparatus in the laser welding of workpieces willnow be described.

The laser beam outputted from the laser oscillator 467 passes throughthe rotary processing head 466 to be applied to the branch pipe-carryingtubular pressure container 471 fixed on the rotary unit 461, and carryout the full-circled welding of the pipe 465 and flange 464.

After the completion of the welding of the pipe 465 and flange 464 toeach other, the rotary unit 461 is turned 90° in the direction of anarrow 470, and the welding of the flange 463 is carried out. The rotaryunit 461 is then further turned 90° to carry out the welding of theflange 462.

According to the welding method of this embodiment, the laser welding offlanges and pipes of a branch pipe-carrying tubular pressure containercan be easily carried out with a laser butt welding of pipe and flangeof not less than 500 mm in diameter. Accordingly, the cost of productionof a branch pipe-carrying tubular pressure container can be greatlyreduced.

FIG. 16 shows the structure of a system which exemplified one embodimentof the laser machining system. In this system, the welding of a trunkpipe and a flange along the bus of a gas insulating control apparatusand the boring of the trunk pipe are accomplished by a laser beam.

A conveyor truck 502 on conveyor rails 501 runs to form a first conveyorline. The aforementioned conveyor truck 502 carries a workpiece or trunkpipe 503 to convey it midway of the first conveyor line in the directionof arrow X₁. Conveyors 504 are arranged at the two sides of the firstconveyor line generally at a right angle with respect to said firstconveyor line to convey flanges 505 to be welded to the two ends of thetrunk pipe 503 in the directions of arrows Y₁ and Y₂, thus forming asecond conveyor line. A number of flange assembling apparatus 506 arearranged at the two sides of the conveyor rail 501 so that it mayassemble the flanges 505 conveyed on the conveyors 504 to the two endsof the aforementioned trunk pipe 503 by changing the directions of theflanges 505. The trunk pipe 503 thus assembled with the flanges 505 bythat flange assembling means 506 is conveyed by the conveyor truck 502on the conveyor rails 501 in the direction of arrow x₂ to a subsequentstep. A positioning device 507 is arranged midway of the conveyor rails501 to rotatably support the trunk pipe 503 conveyed in the direction x₂and assembled with the flanges 505 and to correct the axal gap andradial dislocation of the abutting portions of the flanges 505 and thetrunk pipe 503. A rotary machining apparatus 508 is provided for weldingthe flanged trunk pipe 503 supported by the positioning device 507 tothe flanges 505 and for boring the trunk pipe 503 by using the laserbeam. The rotary machining apparatus 508 has its welding head 508a andboring head 508b arranged rotatably. This rotary machining apparatus 508is supported by a suspender 509 so that it can be moved in thedirections x and y. The welding head 508a and the cutting head 508b canbe moved in the (vertical) direction z and are connected to a laseroscillator 511 through a beam guide 510 with a control unit 512controlling the entire system.

As shown in FIGS. 17 and 18, the rotary machining apparatus 508 includesa plurality of welding and cutting heads 8a to 8d which are arranged ata predetermined spacing on the ends of a rotary disc 513 andconcentrically with a pivot 514. The rotary disc 513 is rotatably drivenby a drive motor 515 fixed on a vertically moving base 516 provided atits one end with a nut engaging with a threaded shaft 518. Thus, theentire apparatus can be vertically moved (in the z direction) by drivinga vertically moving motor 519 connected directly to the threaded shaft518. A dust cover 520, attached to the vertically moving base 516 coversthe optical system 521 of an unused machining head, as shown in FIG. 18to protect the optical system 521 against any dust or anothercontaminants. The optical system 521 is mounted on the rotary disc 513so as to have its optical axis aligned with that of a laser beam 522guided by a beam guide when the laser beam 522 has its path changeddownward by a bend mirror 523.

Next, the positioning device 507 will be described in detail withreference to FIGS. 19, 20 and 21.

FIG. 21 shows a seam portion at the time of the butt welding of thetrunk pipe 503 and the flanges 505. Usually, there arise a widthwise gapg and an external dislocation δ when the trunk pipe 503 and the flanges505 abut against each other. In case of the laser beam welding, theallowable values are set at g≦0.3 mm and δ=0.5 mm. The positioningdevice is used to effect the positioning within the above-specifiedvalues.

As shown in FIGS. 19 and 20, a width adjusting motor 532 is mounted on astationary base 531, with an output shaft of the motor 532 beingconnected to a driving threaded shaft 533 overlaid by a moving base 535which is supported on guide rails 534. On one end of the moving base534, there is mounted a pipe expanding cylinder 537 which is supportedby a bracket 536. To the pipe expanding cylinder 537, there is connecteda hydraulic motor 537a through a hydraulic electromagnetic valve 537b.Moreover, this pipe expanding cylinder 537 has its cylinder rod 538connected to a spline shaft 540 through a coupling 539, and thesecylinder rod 538 and spline shaft 540 are arranged on a common axis.

A pipe rotating motor 542 has its output shaft fixed to a gear 543meshing with a spline bearing 541 for transmitting the rotation andslide.

In front of the aforementioned moving base 535, on the other hand, thereis fixed a support base 544 for supporting the pipe expanding splineshaft. A rotary guide 546 is connected to the support base 544 through abearing 545. A pressure plate 546a for contacting with the end face ofthe flange 505 to be welded to the trunk pipe 503 and a slide guide 547for supporting a pipe expanding core 548 an provided at one end of therotary guide 546. A taper rod 549 which supports the pipe expanding core548 on its sloped side through a slide guide 554 is provided at aleading end of the spline shaft 40.

A flange receiving roller 552 for receiving the flange 505 and a trunkpipe receiving roller 553 for receiving the trunk pipe 503 are fixed tothe stationary base 531.

When the pipe expanding cylinder 537 is retracted by operating thehydraulic electromagnetic valve 537b, the taper rod 549 is retracted,and the pipe expanding core 548 is bulged or expanded. If the pipeexpanding cylinder 537 is advanced, on the other hand, the pipeexpanding core 548 is radially constricted from the center axis. If, therotary motor 542 is rotated in a direction Θ, the spline shaft 540 isrotated through the gear 543 and the spline bearing 541. Simultaneouslywith this, the rotation is also transmitted to the taper rod 549. Sincethe cylinder rod 538 of the pipe expanding cylinder 537 and the splineshaft 540 are connected by the coupling 549 having a built-in bearing,the rotations are blocked here.

If, moreover, the width adjusting motor 532 on the stationary base 531is rotated, the driving threaded shaft 533 is rotated, and the movingbase 535 carried on the slide guide 534 is moved in the direction x ofthe trunk pipe 503 so that the flange contacting plate 546a adjusts thewidthwise positions of the flange 505. At this time, the pipe expandingcylinder 537 in the constricted state is inserted from the ends of thetrunk pipe 503 and the flange 505 supported by their individualreceiving rollers 552 and 553. The pipe expanding cylinder 537 isadvanced, and the expanded pipe is temporarily stopped at the instantwhen the cylinder 537 comes into contact with the inner wall of thetrunk pipe. Then, the width adjusting motor 532 is rotated to move themoving base 535 forward to bring the trunk pipe 503 and the flange 505close to each other. After this, the pipe expanding cylinder 537 isfurther advanced to effect the pipe expansion, which is stopped and heldwhen the dislocation between the flange 505 and the trunk pipe comesinto within the allowable range. Next, the driven motor 542 is rotatedto rotate the trunk pipe 503 and the flange 505 together. After this,the welding is executed by radiating the laser beam from the weldinghead 508a positioned thereabove.

As shown in FIG. 22, a pipe expanding rod 805 and a pipe expanding piece806, which are used to eliminate dislocation between pipes, are insertedin the interior of pipes 801a, 801b to be welded, and height sensors802a, 802b are provided above the outer circumferential surfaces of thepipes 801a, 801b. The signal lines of the height sensors 802a, 802b areconnected to a comparator 803, a signal line of which is connected to ahydraulic cylinder 804 via a hydraulic unit 807. The data concerning theheights h₂, h₁ of the pipes 801a, 801b, the workpieces the edges ofwhich are to be aligned are sent to the comparator 803, in which adifference δ between h₁ and h₂ is calculated. The result of thecalculation is transmitted to the hydraulic unit 807 to operate thehydraulic cylinder 804. Consequently, the pressure in the hydrauliccylinder increases to cause the tapering rod 805 and pipe expandingpiece 806 to be operated, so that the pipes 801a, 801b are subjectedalignment operations. During this operation, the height sensors 802a,802b conduct measurement moment by moment and output signalsrepresentative of the results of the measurement to the comparator 803.This operation is carried out until the difference δ becomes zero. Whenthe difference δ becomes zero, the alignment operations are stopped tocomplete the elimination of the dislocation or misalignment between thepipes.

To enable a measurement of the gap between the opposed edges of a pipe,a flange and a gap eliminating mechanism is provided which includes agap sensor 813 set in a position above the outer circumferentialsurfaces of the opposed edge portions of pipes 801a and 801b, workpiecesto be welded together, and a signal line of the gap sensor is connectedto a comparator 814 so as to drive a hydraulic cylinder 815 through ahydraulic unit 817. A push head 816 is fixed to the front portion of thehydraulic cylinder 815. A gap g between the pipes 801a and 801b, ismeasured at the gap sensor 813, and the data on this measurement aretransmitted to the comparator 814. The hydraulic cylinder 815 isoperated through the hydraulic unit 817 as the gap g is measured, tomove the push head 816 in the X-direction, whereby the gap g can beeliminated. According to this embodiment, the alignment of the opposededges can be carried out automatically when a pipe and a pipe, or a pipeand flange are butt welded together. Therefore, this embodiment producesa large effect when it is applied to a laser welding system.

Next, the operations of the laser machining system according to thepresent invention will be described with reference to FIG. 16.

The present system is directed to the case, in which the trunk pipeforming the bus and the flange to be used in the gas insulation controlsystem are to be welded or in which the trunk pipe is to be bored forbranching. Usually, the bus is used to join the trunk pipe 503 and theflange 505 machined, and the trunk pipe 503 is then machined to have abore for branch pipe, as shown in FIGS. 23a, 23b and 23c. Thesemachining operations are continuously accomplished with the laser beamby using the present system.

First of all, the trunk pipe 503 is carried on and conveyed by theconveyor truck 502 in the direction x₁ until it is positioned andstopped at the center of the flange assembling apparatus 506. At thistime, the flange assembling apparatus 506 has its table surface directedupward. The flanges conveyed by the flange conveyors 504 are grasped onthe table surface of the flange assembling apparatus and are caused toclamp the trunk pipe 503 and turned at 90 degrees so that they areassembled with the trunk pipe 503. The trunk pipe 503 and the flanges505 thus assembled are conveyed by the aforementioned conveyor truck 502to the positions just below the welding head 508a and are positioned atthe center portion of the positioning apparatus 507 for the pipeexpanding, width adjusting and rotating operations. In this positioningapparatus 507, the pipe expanding head is inserted from the two sides ofthe flange 505 to effect the expansion and positioning to predeterminedsizes. After this, the trunk pipe 503 and the flanges 505 arebutt-welded by the laser beam coming from the welding head 508a. Afterthe end of the welding of the two ends of the trunk pipe 503, the laserbeam is switched from the welding head to the cutting head 508b to borethe trunk pipe 503. The flanged trunk pipe thus bored is carried againon the conveyor truck 507 and conveyed to the subsequent step.

According to the present invention, as has been described in variousmanners, the conveyance, positioning, rotations and expansions of theworkpiece can be automated in series when the tubular container composedof the trunk pipe and the flanges is to be manufactured as in the bus ofthe gas insulation control apparatus. As a result, the production costcan be drastically reduced while using one laser oscillator for thewelding and boring operations interchangeably. Thus, it is possible tomanufacture a tubular container having little thermal deformation.

According to the machining apparatus of the present embodiment,moreover, the plural machining heads are arranged on the circumferenceconcentric with the pivot of the rotary disc, and the base of the rotarydrive system is reliably fixed. As a result, it is possible at the timeof indexing rotation to align the optical axis of the laser beamreflected by the bend mirror and the optical axis of the optical systemof the machining heads so that the laser beam can be prevented fromcoming out of focus. Since the machining head left unused is protectedby the dust cover, the optical system can be protected against the dustto invite no trouble at the time of beam condensation.

According to the positioning device of the present invention, all thepipe expanding cores for expanding the trunk pipe from the inside areuniformly moved in the radial directions by the transverse movement ofthe taper rod so that the deformed pipe can be corrected to have a truecircle. Furthermore, the transverse drive source of the taper rod canretain the size of the expanded pipe as it is, if a pilot check valve isdisposed in the hydraulic cylinder and its oil pressure circuit. Then,the size is not changed in the welding operation. If a relief valve inthe oil pressure circuit is used, no hydraulic motor is damaged, even ifit is used as the width adjusting drive source and pressurized even withthe grooves of the tubes being contacting with each other.

In the embodiment of FIGS. 24-26, as shown a base for supporting themachining head is equipped on its lower face with the nozzle 652 havinga variable aperture for spraying the shield gas and the guide 653 foradjusting the diameter of the nozzle 652. The condenser lens 654 isdisposed in the aperture-variable nozzle 652, and the guide 653 isconnected to an air cylinder 655 for moving guide 653 vertically.

On other hand, a nozzle body 656 above the nozzle 652 is formed with ashield gas introduction port 657 which has its leading end connectedwith a three-way electromagnetic valve 658 for interchanging the gases.

The laser beam 622 emitted from the laser oscillator is deflected by thebend mirror 623 into the condenser lens 654 of the machining head. Theaperture-variable nozzle 652 has its tip divided, as shown in FIG. 24.At the lowermost position of the air cylinder 655, the guide 653 alsotakes its lowermost position so that the maximum opening φd_(o) isobtained by the spring action of the aforementioned nozzle 652. When theair cylinder 655 is moved to the uppermost position, on the other hand,the guide 653 constricts the opening of the nozzle 652 to the minimumopening φd_(s), as shown in FIG. 26. In the maximum opening state, O₂gases, for example; can be introduced into the nozzle 652 by opening oneof the inputs of the three-way electromagnetic valve 658. In the minimumopening state, Ar gases can be introduced by opening another input ofthe three-way electromagnetic valve 658.

As has been described hereinbefore, by changing the nozzle diameter ofthe machining head in accordance with the application (for the weldingor cutting operation) and by interchanging the kinds of the gases to besprayed, the cutting and welding operations with the laser can beaccomplished with one head. By the introduction into the laser machiningsystem, moreover, a laser composite machining system can be realized.

To most buses of a gas insulation control apparatus, there are connectednot only the flanges but also the branch pipes. Then, the systemcorresponds to the case in which the cutting and flange-welding of theend faces of the branched pipe are accomplished by the use of the laserbeam.

First of all, the machining process will be schematically described withreference to FIGS. 27a to 27d. The trunk pipe 603 having a branch pipe603a welded thereto in advance (as shown in FIG. 27a) has its pipe endface cut with the laser beam, as shown in FIG. 27b. After this, flanges605, 605' and 605a are assembled to the ends of the trunk pipe 603 andthe branch pipe 603a, as shown in FIG. 27c. After this, the individualflanges 605, 605' and 605a are welded to the individual pipes 603 and603a by the use of the laser beam, as shown in FIG. 12d.

As shown in FIG. 28, the trunk pipe 603, having the branch pipe 603aarc-welded in advance thereto, is conveyed by the conveyor truck 602 onthe conveyor rails 601 to a cutting station A generally constructed of aturntable 660 which can be moved in the y direction and rotated in adirection of a while carrying the branched trunk pipe 603, and a swiveltable 662 which is connected to the laser oscillator 611 through a beamguide 610a and can be rotated in a direction Θ while carrying a cuttinghead 661. Then, the turntable 660 is turned to bring the end of thetrunk pipe 603 or the branch pipe 603a to the cutting position, in whichthe swivel table 662 is rotated while radiating the laser beam from thecutting head 661 to cut the pipe end. When the two ends of the trunkpipe 603 and the end of the branch pipe 603a are cut away, theworkpieces are conveyed to a flange assembling station B constructedsubstantially similar to that of the flange assembling apparatusdescribed with reference to FIG. 16. The trunk pipe 603 having its twoends and its branch pipe 603a assembled with the flanges 605 at theflange assembling station B is conveyed to a welding station C for asubsequent step. If, in this case, the trunk pipe 603 and the branchpipe 603a have an equal diameter, they can be individually assembledwith the flanges 605 on the two conveyors. If the branch pipe 603a has adiameter less than that of the trunk pipe 603, these two pipes can beassembled with the individual flanges by causing one conveyor to carrythe flanges having a diameter matching the diameter of the trunk pipe603 and the other conveyor to carry a flange having a diameter matchingthe diameter of the branch pipe 603a. The welding station C has astructure substantially similar to that of the cutting station A, exceptthat it is equipped with a welding head 663 on the swivel table 662 inplace of the cutting head. Moreover, the trunk pipe 603 or the branchpipe and the flanges 605 and 605a are welded while being irradiated withthe laser beam of the laser oscillator 11 from the welding head 663 byrotating the swivel table 662.

According to the present invention, the machining can be accomplished atthe unit of each member so that the flanges can be welded without anyconsideration into the thermal deformation which might otherwise becaused in the mark welding. Moreover, a machining operation using alarge machine after the laser welding is not required to reduce theproduction cost drastically. Furthermore, the composite machining systemusing the laser can be produced.

While, in the foregoing embodiments, the laser oscillator has beendescribed at being provided for the cutting station and the weldingstation it is understood that the laser oscillator may be shared betweenthe two stations.

We claim:
 1. A machining head comprising: a generally cylindrical nozzlefor guiding a laser beam from a laser oscillator in the vicinity of aworkpiece to be machined; a condensing lens disposed midway in saidnozzle for condensing said laser beam to irradiate said workpiece withthe condensed laser beam; and shield gas introducing means forintroducing a shield gas which is used to shield the laser beam in saidnozzle against a wall surface and which is to be sprayed to saidworkpiece while guiding said laser beam, wherein said nozzle has its tipdivided circumferentially such that divided sectors thereof are radiallyextendible and contractible.
 2. A matching head comprising: a generallycylindrical nozzle for guiding a laser beam from a laser oscillator inthe vicinity of a workpiece to be machined; a condensing lens disposedmidway in said nozzle for condensing said laser beam to irradiate saidworkpiece with the condensed laser beam; shield gas introducing meansfor introducing a shield gas which is used to shield the laser beam insaid nozzle against a wall surface and which is to be sprayed to saidworkpiece while guiding said laser beam; and a guide in the form of anozzle arranged around the outer circumference of the first-named nozzleand made vertically movable while being guided by the outer wall of thefirst-named nozzle such that said nozzle has its tip aperture madevariable by the vertical movements of said guide.
 3. A machining head asset forth in claim 2, wherein said guide further includes a verticaldrive mechanism for moving said nozzle of the guide upward and downward.4. A machining head comprising: a generally cylindrical nozzle forguiding a laser beam from a laser oscillator in the vicinity of aworkpiece to be machined; a condensing lens disposed midway in saidnozzle for condensing said laser beam to irradiate said workpiece withthe condensed laser beam; and shield gas introducing means forintroducing a shield gas which is used to shield the laser beam in saidnozzle against a wall surface and which is to be sprayed to saidworkpiece while guiding said laser beam, wherein said nozzle has its tipdivided circumferentially such that divided sectors thereof are radiallyextendible and contractible, and, and wherein said shield gasintroducing means includes a switch mechanism for switching the shieldgas to be introduced in accordance with the machining application ofsaid workpiece.
 5. A laser machining system comprising: first conveyormeans for conveying a trunk pipe having a branch pipe fixed in advanceto its predetermined portion; a cutting station for cutting the branchedtrunk pipe conveyed by said conveyor means; a flange assembling stationfor assembling each of these ends of said branched trunk pipe conveyedby said first conveyor means, which were cut at said cutting station,with the flange which is conveyed by second conveyor means arrangedgenerally at a right angle with respect to said first conveyor means;and a welding station for welding each of those ends of the branchedtrunk pipe conveyed by said first conveyor means, which were assembledwith a flange at said flange assembling station, and theflange-assembled portion of the same with a laser beam, wherein saidcutting station includes: rails arranged generally at a right angle withrespect to the conveyance direction of said first conveyor means; aturntable made movable on said rails in a direction perpendicular to theconveyance direction of said first conveyor means and turntable in ahorizontal direction; and a swivel table having a swivel axis alignedgenerally with the center axis of said branched trunk pipe to be cut onsaid turntable, so that said swivel table can swing on said swivel axisat a right angle with respect to the turning direction of saidturntable, said swivel table including a cutting head for radiating alaser beam coming from a laser oscillator so as to cut each of the endsof said branched trunk pipe.
 6. A laser machining system comprising:first conveyor means for conveying a trunk pipe having a branch pipefixed in advance to its predetermined portion; a cutting station forcutting the branched trunk pipe conveyed by said conveyor means; aflange assembling station for assembling each of these ends of saidbranched trunk pipe conveyed by said first conveyor means, which werecut at said cutting station, with the flange which is conveyed by secondconveyor means arranged generally at a right angle with respect to saidfirst conveyor means; and a welding station for welding each of thoseends of the branched trunk pipe conveyed by said first conveyor means,which were assembled with a flange at said flange assembling station,and the flange-assembled portion of the same with a laser beam, whereinsaid welding station includes: rails arranged generally at a right anglewith respect to the conveyance direction of said first conveyor means; aturntable made movable on said rails in a direction perpendicular to theconveyance direction of said first conveyor means and turntable in ahorizontal direction; and a swivel table having a swivel axis alignedgenerally with the center axis of the flange-assembled branched trunkpipe to be welded on said turntable, so that said swivel table can swingon said swivel axis at a right angle with respect to the turningdirection of said turntable, said swivel table including a welding headfor radiating a laser beam coming from a laser oscillator so as to weldeach of the ends of said branched trunk pipe and said flange.
 7. Amachining head comprising: a generally cylindrical nozzle for guiding alaser beam from a laser oscillator in the vicinity of a workpiece to bemachined; a condensing lens disposed midway in said nozzle forcondensing said laser beam to irradiate said workpiece with thecondensed laser beam; shield gas introducing means for introducing ashield gas which is used to shield the laser beam in said nozzle againsta wall surface and which is to be sprayed to said workpiece whileguiding said laser beam; and a guide in the form of a nozzle arrangedaround the outer circumference of the first-named nozzle and madevertically movable while being guided by the outer wall of thefirst-named nozzle such that said nozzle has its tip aperture madevariable by the vertical movements of said guide, and wherein saidshield gas introducing means including a switch mechanism for switchingthe shield gas to be introduced in accordance with the machiningapplication of said workpiece.